The Hold Steady's Secret Guest?

I've recently had some mixed experiences with Secret Guests.  Still, It's always fun to try and figure out who it is.

Brooklyn Vegan reported yesterday that The Hold Steady announced a secret special guest to join them at their album release party on May 19th at Bowery.  Catherine then commented that on the French Kiss Records website, they hinted that The Secret Guest will be "a rapper from Minneapolis."

While she speculated that would perhaps be Har Mar Superstar, or the excellent POS, there was only one name that came into my head when I heard Minneapolis and Rapper in the same sentence: Atmosphere.  Slug put on the most enjoyable live hip hop show I had ever seen a few months ago, and it would surely be a treat for anyone who was at the show if he, in fact, where to be the surprise.  Fingers crossed on this one.